852	MINERAL RESOURCES, 1913—PART I.
	which large quantities of metals in ores reported from the mines as shipped in one year may be reported from refineries as produced in marketable form in the following year. For instance, ore shipped in November may be smelted in the following January, and the metal content would be reported from the mines for the calendar year preceding that for which it would be reported in marketable form by the smelters and refineries. The miners furnish the United States Geological Survey with confidential reports on assay values and tonnages of ore and concentrates shipped as the measure of their output, and the mine figures are reported by the Survey so far as possible in terms of recoverable metal; and the smelters and refineries report the metals eventually produced, first as unrefined and finally as refined. In using the mines report it should be noted that tonnages and metal output given are based not on ore mined but on ore treated or sold during the year. Of course most of the ore treated or sold is also mined during the same year, but some of it is necessarily mined during the preceding year. It must not be overlooked also that the mines report aims to give the recoverable content, not the assay content, of ore treated or sold. A part of the actual recovery is, of course, made during the early part of the following year for ores treated or sold late in the year under review, but the basis of the report is essentially metal recovered at whatever time from the tonnage treated or sold during the year covered by the report. For the second and third items enumerated the recovery figures are easily had, as the ore is treated on the ground, and the metal content of the bullion, either base or unrefined, is readily known. In the third item the refining loss and in the fourth item the combined concentrating, smelting, and refining losses must be considered. In the case of the precious metals the concentrating losses may be large and must be allowed for, but the smelting and refining losses are known to be very small and in ordinary practice to be more than offset by certain gains. These gains are of small quantities of pre­cious metals (not paid for, but actually recovered from ores of copper, lead, and zinc) and certain differences in quantity of gold and silver between actual recovery and basis of settlement—-for instance, silver is usually paid for on the basis of 95 per cent of the current New York price and gold at from $19 to $20 per fine ounce. From this it is seen that producers reporting in terms of dollars only will frequently be giving figures corresponding to production below actual final output of metal, and if they erroneously report net proceeds, as they sometimes do, their figures are still further below. Other gains offsetting refining and smelting losses are the relatively small quantities of precious metals, principally gold, not regularly reported from the mines, but coming from transitory placer miners whose production escapes estimate, from stolen ore treated in improvised 'assay offices," and from smelter and refinery cleanings and similar material. Although mine reports in the aggregate may appear, therefore, to give figures of gold and silver that are too high, it is known from actual practice and comparison, later discussed, that final recoveries, especially for gold, are some­what in excess of those reported from the mines.